Field of the Invention
The present invention relates to an object positioning system, a control system, a lithographic apparatus, a method for positioning an object and a method for manufacturing a device.
Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
A lithographic apparatus usually comprises one or more objects that need to be accurately positioned such as a support constructed to support the patterning device and/or a substrate table constructed to hold a substrate. The lithographic apparatus therefore preferably comprises an object positioning system for positioning a moveable object relative to a reference, comprising:
an actuator system configured to apply a force to the object in order to move the moveable object relative to the reference;
a measurement system configured to measure a position of the object relative to the reference; and
a control system configured to position the object relative to the reference based on an output of the measurement system by driving the actuator system.
With the increasing demand for higher throughput, the accelerations applied to the object also increase. This will result in excitation of internal dynamical modes of the object, such as a torsion mode and an umbrella mode. These internal dynamical modes may limit the obtainable accuracy of the object positioning system.